Avalanche Advisory Glossary


Avalanche path A terrain feature in which an avalanche occurs, this is normally split into the start zone, track and runout zone
Avalanche terrain  Any terrain which has the potential to form or be part of a snow avalanche
Bonding  Refers to a snowpack which has undergone some metamorphism and has many links between the individual snow grains, generally leading to a stronger “bonded” snowpack.
Cornice  An overhanging mass of wind sculpted snow projecting beyond the crest of a ridge
Crust  A hard surface layer which can be formed by solar radiation, wind or rain which has the potential to cause instability when buried.
Destructive Scale of Avalanches D1:Too small to bury or injure a person.  Typical mass: less than 10 tons.

D2:Could bury, injure or kill a person.  Typical mass: 100 tons.

D3:Could bury or destroy a car or destroy a small building.  Typical mass: 1000 tons.

D4:Could destroy a railway car, several buildings, or a forest up to 10 acres.  Typical mass: 10,000 tons.

D5:Could destroy a village or forest of 100 acres or more; the largest known avalanches.  Typical mass: 100,000 tons.

Freezing level  The elevation at which the air temperature is at 0° Celsius
Half (1/2)  Used with compass directions, e.g. “lee to the easterly half” refers to the aspects facing west from north through to south.
Instability                                              A weakness or lack of stability indicating that additional loads will result in a given probability of avalanche occurrence.
Lee (leeward)  The side of a mountain protected from the wind
Loose snow  A type of avalanche which originates at a point and spreads out as it descends.
Melt-freeze A metamorphic process when snow changes from a solid to a liquid and back again and may result in the formation of a crust.
Pockets  Small isolated terrain features
Quarter (1/4)  Used with compass directions, e.g. “lee to the easterly quarter” refers to the aspects facing northwest through to southwest.
Runout zone  The area at the bottom of an avalanche path where an avalanche starts to decelerate and comes to rest, this is where the debris is located after an avalanche has occurred.
Safe travel technique                 The use of appropriate terrain to move given the posted danger scale (e.g. stay to ridges and well away from runout zones, or slopes less than 30°)
Shady aspect  The side of a mountain protected from the sun
Slab  A cohesive layer of snow
Sliding hazard  A hazard posed by very hard or icy conditions, also known as ‘slide for life conditions’.
Solar aspect  The side of a mountain exposed to the sun
Start zone  The area at the top of an avalanche path in which unstable snow may fail. Most commonly has an angle greater than 250.
Terrain traps  Terrain features which in the event of an avalanche would compound the effect (e.g. gullies, small bowls)
Track  The area which connects the start zone and runout zone, this can be either confined or unconfined.
Unsupported slope  Slopes which are not being supported by the terrain, e.g convex rolls
Weak layer  A layer in the snowpack identified as a possible failure plane
Wet snow  Snow with a water content greater than 3% and has a temperature of 0° Celsius
Whumphing  The sounds associated with the rapid settlement or collapse of a snowpack, when weighted.
Wind loading  The transport of snow by the wind causing an additional build up of snow on a lee slope
Wind slab  A cohesive layer of snow caused by wind loading
Windward  The side of a mountain exposed to a wind